Advanced Exercises Longest Substring Without Repeating Characters: Write a function to find the length of the longest substring without repeating characters. String Permutations: Write a function to generate all permutations of a given string. String to Integer Conversion: Implement the atoi function, which converts a string to an integer. Longest Common Prefix: Write a function to find the longest common prefix among a list of strings. Balanced Parentheses: Write a function to check if a string has balanced parentheses. Count and Say Sequence: Write a function to generate the nth term of the count$-$and$-$say sequence. Roman to Integer: Write a function to convert a Roman numeral string to an integer. Solutions Outline If you need solutions or hints for any of these exercises, feel free to ask!